This invention relates to a reciprocating piston-type internal combustion engine in which the charging efficiency is increased by causing resonance oscillations of the air or air/fuel mixture (hereafter collectively referred to as "intake gas") as it is introduced into the engine cylinders.
The engine comprises a gas intake conduit assembly which has a feed resonance system including a feed resonator vessel connected directly or by coupling pipes with the respective intake ports of a group of cylinders whose suction strokes do not substantially overlap, if at all. The feed resonance system further has a feed resonance pipe which opens into the feed resonator vessel. The feed resonance pipe has an end which is remote from the feed resonator vessel and which is arranged for receiving the intake gas for charging the associated cylinders. By virtue of the intermittent suction effect of the cylinders, in the feed resonator vessel and the feed resonance pipe intake gas oscillations are generated, as a result of which, in a predetermined resonance rpm range whose magnitude is a function of the dimensions of the intake gas conduit assembly, the degree of charging efficiency of the engine cylinder significantly increases. The frequency of the above-noted intake gas oscillations is significantly lower and their amplitude significantly larger than the sound pressure oscillations or pipe oscillations also generated in the intake gas conduit assembly. Although these last-named oscillations are superposed on the intake air resonance oscillations, their effect is substantially below that of the intake gas resonance oscillations.
The principle and basic solution for the resonance charging of a reciprocating piston-type internal combustion engine are known and are described, for example, in German patent Nos. 1,935,155 and 2,245,732 as well as U.S. Pat. Nos. 3,796,048 and 4,513,699. With the appropriate choice of the dimensions of the feed resonance system it is feasible to obtain the resonance rpm within a desired operational rpm range, particularly in a low rpm range of the engine so that the resonance charging may be combined with an exhaust gas turbocharger whose greatest effect is in the range of the rated rpm. Such a known resonance charging system may find the most effective and advantageous application in six-cylinder in-line engines of such a type where in each instance those three cylinders whose suction strokes do not overlap are in communication with a common feed resonator vessel and the two resonance systems are connected to one another with a compensating vessel into which merge the two feed resonance pipes and which is supplied with intake gas.
In internal combustion engines which have, for example, four cylinders, an effective resonance charging may be achieved by providing for the feed resonance system a closed auxiliary resonator vessel into which merges an auxiliary resonance pipe, whereby an auxiliary resonance system is obtained which communicates with the feed resonance pipe of the feed resonance system by means of an intermediate vessel supplied with intake gas. In such a case the feed resonance system and the auxiliary resonance system are dimensioned relative to one another such that at a predetermined engine rpm at which resonance occurs, the intake gas oscillations in the feed resonance pipe, generated by the intermittent suction strokes of the cylinders, are in phase, whereby the charging efficiency is increased. Stated differently, the movements of intake gas in the feed resonance pipe and the auxiliary resonance pipe coincide in velocity and direction. Such an arrangement is disclosed in German Patent No. 2,949,790, making feasible the smallest possible dimensioning for the intermediate vessel so that despite the limited space in the zone of the engine, the intermediate vessel may be accommodated without difficulties.
In all known embodiments of intake gas resonance systems there exists a predetermined resonance frequency which may be tuned to the desired operational rpm range by an appropriate design of the dimensions of the resonator vessels and resonance pipes. An rpm-dependent alteration of the resonance frequency may, however, also be achieved by altering the dimensions of the resonance system in an rpm-dependent manner. From Japanese Utility Model No. 59 22 249 it is known to vary the resonance pipe length as a function of the rpm. It is further known to provide one wall of the resonator vessel with a bounding piston which adjusts the volume of the resonator vessel as a function of the rpm. According to German Offenlegungsschrift (Non-examined Published Application) No. 3,314,911 two resonance pipes are interconnected by means of a short coupling conduit in which a butterfly valve is arranged which may be set in an rpm-dependent manner such that as a result of an opening or a closing of the butterfly valve two different resonance frequencies are obtained. For improving the torque characteristics the regulating and setting devices necessary for obtaining different resonance frequencies tend to be prohibitively expensive when compared with the achievable advantages and also, structural and operational difficulties may arise.